update readme.md
update readme.md

New section about how to contribute

alinanmorariu/styleguide,blandine/styleguide,blandine/styleguide,GrayOverride/styleguide,Teleopti/styleguide,Teleopti/styleguide,tiaoshi/styleguide,GanHZ/styleguide,alinanmorariu/styleguide,GanHZ/styleguide,tiaoshi/styleguide,zhengl/styleguide,alinanmorariu/styleguide,zhengl/styleguide,zhengl/styleguide,GrayOverride/styleguide,GrayOverride/styleguide,blandine/styleguide,GanHZ/styleguide,tiaoshi/styleguide